Method for estimating charge air cooler condensation storage with an intake oxygen sensor

ABSTRACT

Methods and systems are provided for estimating water storage in a charge air cooler (CAC). In one example, an amount of water accumulating in the CAC may be based on an output of an oxygen sensor positioned downstream of the CAC and ambient humidity. Further, engine actuators may be adjusted to purge condensate from the CAC and/or reduce condensate formation based on the amount of water inside the CAC.

BACKGROUND/SUMMARY

Turbocharged and supercharged engines may be configured to compressambient air entering the engine in order to increase power. Compressionof the air may cause an increase in air temperature, thus, anintercooler or charge air cooler (CAC) may be utilized to cool theheated air thereby increasing its density and further increasing thepotential power of the engine. Condensate may form in the CAC when theambient air temperature decreases, or during humid or rainy weatherconditions, where the intake air is cooled below the water dew point.Condensate may collect at the bottom of the CAC, or in the internalpassages, and cooling turbulators. Under certain air flow conditions,condensate may exit the CAC and enter an intake manifold of the engineas water droplets. If too much condensate is ingested by the engine,engine misfire and/or combustion instability may occur.

Other attempts to address engine misfire due to condensate ingestioninclude avoiding condensate build-up. In one example, the coolingefficiency of the CAC may be decreased in order to reduce condensateformation. However, the inventors herein have recognized potentialissues with such methods. Specifically, while some methods may reduce orslow condensate formation in the CAC, condensate may still build up overtime. If this build-up cannot be stopped, ingestion of the condensateduring acceleration may cause engine misfire. Additionally, in anotherexample, engine actuators may be adjusted to increase combustionstability during condensate ingestion. In one example, the condensateingestion may be based on a mass air flow rate and amount of condensatein the CAC; however, these parameters may not accurately reflect theamount of water in the charge air exiting the CAC and entering theintake manifold. As a result, engine misfire and/or unstable combustionmay still occur.

In one example, the issues described above may be addressed by a methodfor adjusting engine actuators based on water storage at a charge aircooler (CAC), the water storage based on an output of an oxygen sensorpositioned downstream of the CAC and ambient humidity. Specifically, theoxygen sensor may be positioned at an outlet of the CAC. An enginecontroller may use the output of the oxygen sensor to determine waterstorage at the CAC. In one example, water storage may include one ormore of a water storage amount or a water storage rate (e.g., wateraccumulation rate within the CAC). The engine controller may then adjustengine operation to increase combustion stability, decrease condensateformation in the CAC, and/or evacuate condensate from the CAC inresponse to the determined water storage values. As a result, condensateformation within the CAC may be reduced and engine misfire andcombustion instability due to water ingestion may be decreased.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an example engine system including acharge air cooler.

FIG. 2 is a flow chart of a method for operating an oxygen sensor todetermine water storage at a charge air cooler.

FIG. 3 is a flow chart of a method for adjusting engine operation basedon water storage at a charge air cooler.

FIG. 4 show graphs illustrating example adjustments to engine operationbased on water storage at a charge air cooler.

DETAILED DESCRIPTION

The following description relates to systems and methods for estimatingwater storage in a charge air cooler (CAC) in an engine system, such asthe system of FIG. 1. A first oxygen sensor may be positioned at anoutlet of the CAC. In one example, the oxygen sensor may be a variablevoltage intake oxygen sensor which may operate between a variablevoltage (VVs) mode and a base mode. A method for operating the firstoxygen sensor to determine water storage at the CAC is shown in FIG. 2.Specifically, a water storage amount, or amount of water accumulatedwithin the CAC, may be determined based on an output of the first oxygensensor and ambient humidity. The first oxygen sensor may be differentthan a second intake oxygen sensor positioned within the intake manifoldto determine EGR flow. An engine controller may adjust engine operationbased on the water storage amount, as shown at FIG. 3. Adjusting engineoperation may include adjusting engine actuators to decrease a coolingefficiency of the CAC, purge condensate from the CAC, and/or increasecombustion stability during ingestion of water by the engine. FIGS. 4A-Bshow example engine actuator adjustments based on water storage at theCAC. In this way, positioning a first oxygen sensor at the outlet of theCAC may allow for the determination of condensate storage in the CAC.Engine actuator adjustments based on condensate storage may thendecrease condensate formation in the CAC, increase combustion stabilityduring condensate purging from the CAC, and/or decrease water storagewithin the CAC.

FIG. 1 is a schematic diagram showing an example engine 10, which may beincluded in a propulsion system of an automobile. The engine 10 is shownwith four cylinders or combustion chambers 30. However, other numbers ofcylinders may be used in accordance with the current disclosure. Engine10 may be controlled at least partially by a control system including acontroller 12, and by input from a vehicle operator 132 via an inputdevice 130. In this example, the input device 130 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Each combustion chamber (e.g.,cylinder) 30 of the engine 10 may include combustion chamber walls witha piston (not shown) positioned therein. The pistons may be coupled to acrankshaft 40 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. The crankshaft 40 may becoupled to at least one drive wheel of a vehicle via an intermediatetransmission system 150. Further, a starter motor may be coupled tocrankshaft 40 via a flywheel to enable a starting operation of engine10. The crankshaft 40 may also be used to drive an alternator (not shownin FIG. 1).

An engine output torque may be transmitted to a torque converter (notshown) to drive the automatic transmission system 150. Further, one ormore clutches may be engaged, including forward clutch 154, to propelthe automobile. In one example, the torque converter may be referred toas a component of the transmission system 150. Further, transmissionsystem 150 may include a plurality of gear clutches 152 that may beengaged as needed to activate a plurality of fixed transmission gearratios. Specifically, by adjusting the engagement of the plurality ofgear clutches 152, the transmission may be shifted between a higher gear(that is, a gear with a lower gear ratio) and a lower gear (that is, agear with a higher gear ratio). As such, the gear ratio differenceenables a lower torque multiplication across the transmission when inthe higher gear while enabling a higher torque multiplication across thetransmission when in the lower gear. The vehicle may have four availablegears, where transmission gear four (transmission fourth gear) is thehighest available gear and transmission gear one (transmission firstgear) is the lowest available gear. In other embodiments, the vehiclemay have more or less than four available gears. As elaborated herein, acontroller may vary the transmission gear (e.g., upshift or downshiftthe transmission gear) to adjust an amount of torque conveyed across thetransmission and torque converter to vehicle wheels 156 (that is, anengine shaft output torque).

As the transmission shifts to a lower gear, the engine speed (Ne or RPM)increases, increasing engine airflow. An intake manifold vacuumgenerated by the spinning engine may be increased at the higher RPM. Insome examples, as discussed further below, downshifting may be used toincrease engine airflow and purge condensate built up in a charge aircooler (CAC) 80.

The combustion chambers 30 may receive intake air from the intakemanifold 44 and may exhaust combustion gases via an exhaust manifold 46to an exhaust passage 48. The intake manifold 44 and the exhaustmanifold 46 can selectively communicate with the combustion chamber 30via respective intake valves and exhaust valves (not shown). In someembodiments, the combustion chamber 30 may include two or more intakevalves and/or two or more exhaust valves.

Fuel injectors 50 are shown coupled directly to the combustion chamber30 for injecting fuel directly therein in proportion to the pulse widthof signal FPW received from controller 12. In this manner, the fuelinjector 50 provides what is known as direct injection of fuel into thecombustion chamber 30; however it will be appreciated that portinjection is also possible. Fuel may be delivered to the fuel injector50 by a fuel system (not shown) including a fuel tank, a fuel pump, anda fuel rail.

In a process referred to as ignition, the injected fuel is ignited byknown ignition means such as spark plug 52, resulting in combustion.Spark ignition timing may be controlled such that the spark occursbefore (advanced) or after (retarded) the manufacturer's specified time.For example, spark timing may be retarded from maximum break torque(MBT) timing to control engine knock or advanced under high humidityconditions. In particular, MBT may be advanced to account for the slowburn rate. In one example, spark may be retarded during a tip-in. In analternate embodiment, compression ignition may be used to ignite theinjected fuel.

The intake manifold 44 may receive intake air from an intake passage 42.The intake passage 42 includes a throttle 21 having a throttle plate 22to regulate flow to the intake manifold 44. In this particular example,the position (TP) of the throttle plate 22 may be varied by thecontroller 12 to enable electronic throttle control (ETC). In thismanner, the throttle 21 may be operated to vary the intake air providedto the combustion chambers 30. For example, the controller 12 may adjustthe throttle plate 22 to increase an opening of the throttle 21.Increasing the opening of the throttle 21 may increase the amount of airsupplied to the intake manifold 44. In an alternate example, the openingof the throttle 21 may be decreased or closed completely to shut offairflow to the intake manifold 44. In some embodiments, additionalthrottles may be present in intake passage 42, such as a throttleupstream of a compressor 60 (not shown).

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system may route a desired portion of exhaust gas from the exhaustpassage 48 to the intake passage 42 via an EGR passage, such as highpressure EGR passage 140. The amount of EGR provided to the intakepassage 42 may be varied by the controller 12 via an EGR valve, such ashigh pressure EGR valve 142. Under some conditions, the EGR system maybe used to regulate the temperature of the air and fuel mixture withinthe combustion chamber. FIG. 1 shows a high pressure EGR system whereEGR is routed from upstream of a turbine of a turbocharger to downstreamof a compressor of a turbocharger through EGR passage 140. FIG. 1 alsoshows a low pressure EGR system where EGR is routed from downstream ofturbine of a turbocharger to upstream of a compressor of a turbochargerthrough low pressure EGR passage 157. A low pressure EGR valve 155 maycontrol the amount of EGR provided to the intake passage 42. In someembodiments, the engine may include both a high pressure EGR and a lowpressure EGR system, as shown in FIG. 1. In other embodiments, theengine may include either a low pressure EGR system or a high pressureEGR system. When operable, the EGR system may induce the formation ofcondensate from the compressed air, particularly when the compressed airis cooled by the charge air cooler, as described in more detail below.

The engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 60 arrangedalong the intake passage 42. For a turbocharger, the compressor 60 maybe at least partially driven by a turbine 62, via, for example a shaft,or other coupling arrangement. The turbine 62 may be arranged along theexhaust passage 48. Various arrangements may be provided to drive thecompressor. For a supercharger, the compressor 60 may be at leastpartially driven by the engine and/or an electric machine, and may notinclude a turbine. Thus, the amount of compression provided to one ormore cylinders of the engine via a turbocharger or supercharger may bevaried by the controller 12.

In the embodiment shown in FIG. 1, the compressor 60 may be drivenprimarily by the turbine 62. The turbine 62 may be driven by exhaustgases flowing through the exhaust passage 48. Thus, the driving motionof the turbine 62 may drive the compressor 60. As such, the speed of thecompressor 60 may be based on the speed of the turbine 62. As the speedof the compressor 60 increases, more boost may be provided through theintake passage 42 to the intake manifold 44.

Further, the exhaust passage 48 may include a wastegate 26 for divertingexhaust gas away from the turbine 62. Additionally, the intake passage42 may include a compressor bypass or recirculation valve (CRV) 27configured to divert intake air around the compressor 60. The wastegate26 and/or the CRV 27 may be controlled by the controller 12 to be openedwhen a lower boost pressure is desired, for example. For example, inresponse to compressor surge or a potential compressor surge event, thecontroller 12 may open the CBV 27 to decrease pressure at the outlet ofthe compressor 60. This may reduce or stop compressor surge.

The intake passage 42 may further include a charge air cooler (CAC) 80(e.g., an intercooler) to decrease the temperature of the turbochargedor supercharged intake gases. In some embodiments, the CAC 80 may be anair to air heat exchanger. In other embodiments, the CAC 80 may be anair to liquid heat exchanger. The CAC 80 may also be a variable volumeCAC. Hot charge air (boosted air) from the compressor 60 enters theinlet of the CAC 80, cools as it travels through the CAC, and then exitsto pass through the throttle 21 and then enter the engine intakemanifold 44. Ambient air flow from outside the vehicle may enter engine10 through a vehicle front end and pass across the CAC, to aid incooling the charge air. Condensate may form and accumulate in the CACwhen the ambient air temperature decreases, or during humid or rainyweather conditions, where the charge air is cooled below the water dewpoint temperature. Further, when the charge air entering the CAC isboosted (e.g., boost pressure and/or CAC pressure is greater thanatmospheric pressure), condensate may form if the CAC temperature fallsbelow the dew point temperature. When the charge air includesrecirculated exhaust gasses, the condensate can become acidic andcorrode the CAC housing. The corrosion can lead to leaks between the aircharge, the atmosphere, and possibly the coolant in the case ofwater-to-air coolers. Further, if condensate builds up in the CAC, itmay be ingested by the engine during times of increased airflow. As aresult, unstable combustion and/or engine misfire may occur.

The engine 10 may further include one or more oxygen sensors positionedin the intake passage 42. As such, the one or more oxygen sensors may bereferred to as intake oxygen sensors. In the depicted embodiment, afirst oxygen sensor 162 is positioned downstream of the CAC 80. In oneexample, the first oxygen sensor 162 may be positioned at an outlet ofthe CAC 80. As such, the first oxygen sensor 162 may be referred toherein as the CAC outlet oxygen sensor. In another example, the firstoxygen sensor 162 may be positioned downstream of the CAC 80 outlet. Insome embodiments, as shown in FIG. 1, an optional second oxygen sensor164 may be positioned in the intake manifold 44. As described furtherbelow, the second oxygen sensor 164 may be used to estimate EGR flow. Inanother embodiment, the second oxygen sensor 164 may be positioned inthe intake passage 42 downstream of the compressor 60 and the EGRpassage 140 (or EGR passage 157 if the engine only includes low pressureEGR). In yet other embodiments, a third oxygen sensor may be positionedat the inlet of the CAC.

Intake oxygen sensors 162 and/or 164 may be any suitable sensor forproviding an indication of the oxygen concentration of the charge air(e.g., air flowing through the intake passage 42), such as a linearoxygen sensor, intake UEGO (universal or wide-range exhaust gas oxygen)sensor, two-state oxygen sensor, etc. In one example, the intake oxygensensors 162 and/or 164 may be an intake oxygen sensor including a heatedelement as the measuring element. During operation, a pumping current ofthe intake oxygen sensor may be indicative of an amount of oxygen in thegas flow.

In another example, the intake oxygen sensor 162 and/or 164 may be avariable voltage (variable Vs or VVs) intake oxygen sensor wherein areference voltage of the sensor may be modulated between a lower or basevoltage at which oxygen is detected and a higher voltage at which watermolecules in the gas flow may be dissociated. For example, during baseoperation, the intake oxygen sensor may operate at the base referencevoltage. At the base reference voltage, when water hits the sensor, theheated element of the sensor may evaporate the water and measure it as alocal vapor or diluent. This operational mode may be referred to hereinas the base mode. The intake oxygen sensor may also operate in a secondmode wherein the reference voltage is increased to a second referencevoltage. The second reference voltage may be higher than the basereference voltage. Operating the intake oxygen sensor at the secondreference voltage may be referred to herein as variable Vs (VVs) mode.When the intake oxygen sensor operates in VVs mode, the heated elementof the sensor dissociates water in the air and subsequently measures thewater concentration. In this mode, the pumping current of the sensor maybe indicative of an amount of oxygen in the gas flow plus an amount ofoxygen from dissociated water molecules. However, if the referencevoltage is further increased, additional molecules, such as CO₂, mayalso be dissociated and the oxygen from these molecules may also bemeasured by the sensor. In a non-limiting example, the lower, basereference voltage may be 450 mV and the higher, second reference voltagemay be greater than 950 mV. However, in the method presented at FIG. 2for determining an amount of water in the charge air, the secondreference voltage may be maintained lower than a voltage at which CO₂may also be dissociated. In this way, the second reference voltage maybe set such that only oxygen from water (and not CO₂) may be measured inVVs mode.

The first oxygen sensor 162 may be used to estimate condensate or waterstorage at the CAC 80. As discussed further below with reference to FIG.2, the oxygen concentration in the air leaving the CAC 80 (e.g.,determined by first oxygen sensor 162) may be used to determine aconcentration of water within the CAC 80. Various methods may be used toestimate water in the CAC 80. For example, the intake oxygen sensor maymeasure an amount of oxygen in the charge air and then estimate anamount of water in the charge air using a dilution method. If the intakeoxygen sensor is a VVs intake oxygen sensor, the sensor may estimate anamount of water in the charge air using a dissociation method (e.g.,operating in VVs mode and modulating between a base reference voltageand a higher, second reference voltage). Both of these methods formeasuring and/or estimating an amount of water in the charge air arediscussed further below.

A first method for estimating water in the charge air using an intakeoxygen sensor includes the dilution method. When using the dilutionmethod, the intake oxygen sensor may be operated in the base mode at thebase reference voltage. In one example, the base reference voltage maybe 450 mV. In another example, the base reference voltage may be avoltage larger or smaller than 450 mV. The intake oxygen sensor may takea measurement and determine an amount of oxygen in the gas (e.g., intakeor charge air) based on a pumping current of the sensor. Then, acomparison of the measured concentration of oxygen vs. the amount of airmay be used to determine the amount of water as a diluent in the chargeair. The dilution method may give an inaccurate water estimate if thediluent includes substances other than water, such as EGR and/or fuelvapor.

A second method for estimating water in the charge air using an intakeoxygen sensor includes the dissociation method. Specifically, for thedissociation method, a VVs intake oxygen sensor may operate in VVs modewherein the reference voltage is increased from the base referencevoltage to the higher, second reference voltage. In one example, thesecond reference voltage may be 950 mV. In another example, the secondreference voltage may be a voltage greater than 950 mV. However, thesecond reference voltage may be maintained at a voltage lower than thevoltage at which CO₂ is dissociated by the sensor. In VVs mode, theintake oxygen sensor dissociates the water into hydrogen and oxygen andmeasures the amount of oxygen from dissociated water molecules inaddition to the amount of oxygen in the gas. By taking the differencebetween the measurements at the second reference voltage and the basereference voltage, an estimate of the total water concentration in thecharge air may be determined. Additionally, at each temperaturecondition at the outlet of the CAC, a different amount of saturatedwater may be produced. If the saturation water at the CAC outlettemperature condition is known (e.g., in a look-up table stored in thecontroller), the controller 12 may subtract this value from the totalwater concentration measured by the intake oxygen sensor to determine anamount water in the charge air in the form of water droplets. Forexample, the saturation water at the CAC outlet temperature conditionmay include a mass of water at the saturation vapor pressure conditionat the CAC outlet. In this way, the controller may determine an amountof liquid water in the charge air exiting the CAC from intake oxygensensor measurements.

Additionally, in both methods (e.g., dilution and dissociation) ofestimating water in the charge air exiting the CAC, the oxygenconcentration measurement from the intake oxygen sensor (IAO2) (e.g.,sensor output of first oxygen sensor 162) may be adjusted based onadditional diluents in the charge air such as purge vapors (e.g., fromfuel canister purge events), positive crankcase ventilation flow (PCV),or the like. In some embodiments, correction factors for purge and/orPCV flow may be pre-determined for different engine operatingconditions. The correction factors may then be used to adjust the outputof the IAO2 before estimating the water concentration. As a result, anydecrease in oxygen concentration from purge or PCV flow may be correctedfor with the correction factor. This may result in a more accurate waterestimate.

Additionally, by taking a difference between an estimate of waterentering the CAC and water exiting the CAC (determined by the output offirst oxygen sensor 162), the amount of water stored (e.g.,accumulating) within the CAC may be determined. The amount of waterentering the CAC may be approximated by ambient humidity. In oneexample, ambient humidity may be measured with an ambient humiditysensor. In another example, ambient humidity may be estimated based onintake temperature, intake pressure, and/or a windshield wiper dutycycle. In yet another example, ambient humidity may be determined basedon information from local weather stations or using the IAO2 sensorreading when EGR is not flowing and no impact of PCV or purge exists(e.g., during no PCV or purge flow). For example, the ambient humidityis determined as specified only when low-pressure EGR in not flowingand/or during conditions without any low pressure EGR flow. In otherexamples the engine does not include low pressure EGR. Thus, a wateraccumulation rate in the CAC may be determined from the differencebetween ambient humidity and the water concentration of the CAC outletair as determined from the output of the first oxygen sensor 162.Further, an amount of water within the CAC may be determined based onthe water accumulation rate over a period of time. In some examples,estimating water inside the CAC in this way may only be performed whenEGR is not flowing. Said another way, water estimates at the CAC basedon ambient humidity and the output of the first oxygen sensor 162 mayonly be accurate when EGR is turned off or below a threshold rate, thethreshold rate based on an EGR flow rate that may not significantlychange the oxygen sensor output. As discussed further below, if EGR isflowing, alternate methods of estimating water accumulation in the CACmay be used.

The controller 12 may use measurements at the first oxygen sensor 162and an ambient humidity value (estimated or measured) to determine awater storage rate and/or water storage amount in the CAC 80 (e.g.,amount of water accumulated within the CAC 80). For example, an amountof water stored in the CAC 80 may be estimated from measurements fromthe first oxygen sensor 162 positioned at the CAC outlet. The controller12 may determine the water storage amount by one or more of the methodsdescribed above (e.g., dilution or dissociation method). In anotherexample, an amount of water released from the CAC may be determined frommeasurements from the first oxygen sensor 162.

In response to water storage estimates, the controller 12 may adjustengine actuators to adjust combustion parameters, activate condensatepurging routines, and/or adjust actuators to increase or decrease CACcooling efficiency. Engine actuator adjustments in response to waterstorage measurements from the oxygen sensors is presented in furtherdetail below at FIG. 3.

The second oxygen sensor 164 may be used to determine EGR flow. Forexample, controller 12 may estimate the percent dilution of the EGR flowbased on feedback from the second oxygen sensor 164. In some examples,the controller 12 may then adjust one or more of EGR valve 142, EGRvalve 155, throttle 21, CRV 27, and/or wastegate 26 to achieve a desiredEGR dilution percentage of the intake air. Thus, in this example, thefirst oxygen sensor 162 is different from the second oxygen sensor 164used to estimate EGR flow. In other examples, EGR flow may be determinedfrom the first oxygen sensor 162.

The controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. The controller 12 may receivevarious signals from sensors coupled to the engine 10 for performingvarious functions to operate the engine 10. In addition to those signalspreviously discussed, these signals may include measurement of inductedmass air flow from MAF sensor 120; engine coolant temperature (ECT) fromtemperature sensor 112, shown schematically in one location within theengine 10; a profile ignition pickup signal (PIP) from Hall effectsensor 118 (or other type) coupled to crankshaft 40; the throttleposition (TP) from a throttle position sensor, as discussed; andabsolute manifold pressure signal, MAP, from sensor 122, as discussed.Engine speed signal, RPM, may be generated by the controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold 44. Note that various combinations of the above sensorsmay be used, such as a MAF sensor without a MAP sensor, or vice versa.During stoichiometric operation, the MAP sensor can give an indicationof engine torque. Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, the Hall effect sensor 118, which is alsoused as an engine speed sensor, may produce a predetermined number ofequally spaced pulses every revolution of the crankshaft 40.

Other sensors that may send signals to controller 12 include atemperature and/or pressure sensor 124 at an outlet of a charge aircooler 80, the first oxygen sensor 162, the second oxygen sensor 164,and a boost pressure sensor 126. Other sensors not depicted may also bepresent, such as a sensor for determining the intake air velocity at theinlet of the charge air cooler, and other sensors. In some examples,storage medium read-only memory chip 106 may be programmed with computerreadable data representing instructions executable by microprocessorunit 102 for performing the methods described below as well as othervariants that are anticipated but not specifically listed. Exampleroutines are described herein at FIGS. 2-3.

The system of FIG. 1 provides for an engine system including an intakemanifold, a charge air cooler positioned upstream of the intakemanifold, an oxygen sensor positioned at an outlet of the charge aircooler, and a controller with computer readable instructions foradjusting engine operation responsive to water storage at the charge aircooler, the water storage based on an output of the oxygen sensor andambient humidity when EGR is not flowing. In one example, adjustingengine operation includes one or more of adjusting spark timing, massair flow, vehicle grille shutters, engine cooling fans, a charge aircooler coolant pump, and/or downshifting a transmission gear. Further,water storage includes one or more of a water storage amount in thecharge air cooler or a water storage rate in the charge air cooler.

FIG. 2 shows a method 200 for operating an oxygen sensor to determinewater storage at the CAC. Specifically, the oxygen sensor may be anoxygen sensor positioned proximate to an outlet of the CAC. In oneexample, the method 200 is executable by the controller 12 shown inFIG. 1. The method 200 may be used in an engine system in which anoxygen sensor at the outlet of the CAC (such as first oxygen sensor 162shown in FIG. 1) and ambient humidity is used to determine water storageparameters at the CAC. In one example, the oxygen sensor is a VVs oxygensensor capable of modulating between two reference voltages. In anotherexample, the oxygen sensor may not be a VVs sensor and may estimatewater storage at the CAC using a dilution method.

The method begins at 202 by estimating and/or measuring engine operatingconditions. Engine operating conditions may include engine speed andload, EGR flow rate, mass air flow rate, conditions of the charge aircooler (e.g., inlet and/or outlet temperature and pressures), ambienthumidity, ambient temperature, torque demand, etc. At 204, the methodincludes determining if EGR is turned off (e.g., EGR is not flowing). Asdiscussed above, if EGR is flowing, the oxygen concentration determinedby the oxygen sensor may decrease, thereby decreasing the accuracy ofthe water estimate. Thus, if EGR is not turned off, the method continuesto 205 to estimate water storage at the CAC using an alternate method.Said another way, if EGR is flowing, water storage at the CAC may not beestimated using the oxygen sensor output and ambient humidity.

However, if EGR is turned off and not flowing, the method continues onto 206 to estimate the total water concentration in the charge airexiting the CAC based on the output of the oxygen sensor positioned atthe CAC outlet (e.g., positioned downstream from the CAC). In oneexample, the water concentration in the charge air may be estimated fromthe oxygen sensor output using the dilution method. As discussed above,the dilution method may include measuring the amount of oxygen in thecharge air exiting the CAC outlet. Assuming the diluent in the chargeair is water, the controller may determine the amount of water in thecharge air based on the concentration of oxygen in air vs. theconcentration of oxygen measured in the charge air (with the oxygensensor positioned at the CAC outlet). Since the oxygen sensor may bepositioned at the CAC outlet, the amount of water in the charge air maybe an estimate of the water release amount from the CAC.

In another example, the water concentration in the charge air may beestimated from the oxygen sensor output using the dissociation method(if the oxygen sensor is a VVs oxygen sensor). As discussed above, thedissociation method may include increasing the reference voltage of theoxygen sensor from a base, first voltage to a second voltage. The methodmay further include determining a change in pumping current between thebase reference voltage and the second reference voltage. As describedabove, the change in pumping current may be indicative of the amount ofoxygen in the gas and the amount of oxygen dissociated from watermolecules in the gas (e.g., charge air). The total water (e.g.,condensate) concentration in the charge air (e.g., in the charge air atthe CAC outlet) may then be determined based on the change in pumpingcurrent. In some examples, an amount of liquid water (e.g., waterdroplets) in the charge air at the CAC outlet (e.g., exiting the CAC)may then be determined by subtracting a saturation water value for theCAC outlet temperature from the total water concentration. Thesaturation water values may include a mass of water at the saturationvapor pressure condition at the CAC outlet. As discussed above, thecontroller may determine the saturation water value from a look-up tableof saturation water values at various CAC outlet temperatures stored inthe controller.

At 210, the method includes determining a difference between ambienthumidity and the total water concentration in the charge air at the CACoutlet in order to determine a water storage amount at (e.g., inside of)the CAC. As discussed above, the ambient humidity may be an estimated ormeasured value determined from one or more of a humidity sensor, weatherdata (received from a weather station, remote device, in-vehicleentertainment and communications system, etc.), intake temperature,intake pressure, and/or a windshield wiper duty cycle. The ambienthumidity may give an estimate of water entering the CAC. Thus, a wateraccumulation rate (e.g., water storage rate) within the CAC may besubstantially equal to the difference between the ambient humidity andwater concentration at the CAC outlet (e.g., the water measurement fromthe oxygen sensor at the CAC outlet). Then, the method at 210 may alsoinclude determining the amount of water accumulated in the CAC based onthe water storage rate over a period of time.

If the difference between the ambient humidity and the waterconcentration at the CAC outlet (determined at 208 and 210) is positive(e.g., ambient humidity greater than the water concentration at the CACoutlet), then water is being stored in the CAC. Alternatively, if thedifference between the ambient humidity and the water concentration atthe CAC outlet is negative (e.g., ambient humidity less than the waterconcentration at the CAC outlet), then water is being released from theCAC. In some examples, the method may also include estimating a waterrelease amount and/or rate based on the output of the oxygen sensor atthe CAC outlet and ambient humidity. In this way, a negative waterstorage rate may indicate a positive water release rate from the CAC.The water release rate may be further based on a saturation water valuefor the CAC outlet temperature from the total water concentration. Thesaturation water values may include a mass of water at the saturationvapor pressure condition at the CAC outlet. In one example, thecontroller may determine the saturation water value from a look-up tableof saturation water values at various CAC outlet temperatures stored inthe controller.

At 212, the controller may adjust engine actuators based on the waterstorage rate or amount determined at 210. In some examples, thecontroller may additionally or alternatively adjust engine actuatorsbased on the water release rate and/or amount from the CAC. A method foradjusting engine actuators responsive to water storage is presented atFIG. 3.

In this way, a method may include adjusting engine operation responsiveto water content in an intake system, the water content based on anoutput of an intake oxygen sensor wherein a reference voltage of theintake oxygen sensor is adjusted between a first voltage and a secondvoltage. As described above, an oxygen sensor may be positioned withinan intake system (e.g., intake passage 42 and/or intake manifold 44shown in FIG. 1). In one example, the intake oxygen sensor may bepositioned at a CAC outlet. In another example, the intake oxygen sensormay be positioned at another location in the intake system such asdownstream of the CAC. A reference voltage of the intake oxygen sensormay be adjusted, or modulated, between a first voltage and a secondvoltage, the second voltage being greater than the first voltage. Thefirst voltage may be a voltage at which a concentration of oxygen in theintake air may be determined, for example, while the second voltage maybe a voltage at which water molecules may be dissociated. A differencein a pumping current of the intake oxygen sensor at the first voltageand second voltage may be indicative of water content in the intakesystem. Engine operation, such as spark timing, airflow, etc., may thenbe adjusted response to the water content determined at the intakeoxygen sensor.

Turning now to FIG. 3, a method 300 is shown for adjusting engineactuators and/or engine operation based on water storage in the CAC. Inone example, the method 300 is executable by the controller 12 shown inFIG. 1. Method 300 begins at 302 by obtaining oxygen sensor data fromone or more oxygen sensors. The one or more oxygen sensors may includean oxygen sensor positioned proximate to the outlet of the CAC (e.g.,first oxygen sensor 162 shown in FIG. 1). For example, the method at 302may include obtaining CAC water storage data or parameters determined inmethod 200, presented at FIG. 2. The water storage parameters mayinclude one or more of a water storage rate (e.g., rate of wateraccumulating within the CAC) and/or a water storage amount (e.g., amountof water stored in the CAC). In some examples, the water storageparameters may further include a water release rate and/or amount.

At 303, the method includes determining if the water storage rate ispositive. As described at FIG. 2, the water storage rate may be based ona difference between ambient humidity and the water concentration at theCAC outlet (based on oxygen sensor output). If ambient humidity isgreater than the water concentration at the CAC outlet (e.g., watercontent at CAC inlet greater than water content at CAC outlet), thenwater is being stored in the CAC and the water storage rate is positive.Conversely, if the ambient humidity is less than the water concentrationat the CAC outlet (e.g., water content at the CAC outlet greater thanwater content at the CAC inlet), then water is being released from theCAC and the water storage rate may be negative. Even though the waterstorage rate may be negative, the net amount of condensate within theCAC may still be greater than zero. In some examples wherein the ambienthumidity is substantially equal to the water concentration at the CACoutlet, the water storage rate may be substantially zero such that nowater is being released or stored within the CAC. The amount of water inthe CAC may then be determined based on previous water storage rate dataover a period of time.

If the water storage rate is negative at 303, the method continues on to314 to indicate that water is being released from the CAC. In responseto the negative water storage rate (e.g., ambient humidity being lessthan the water concentration of the charge air at the CAC outlet), themethod continues on to 316 to adjust combustion parameters and/or limitairflow to the engine. In one example, adjusting combustion parametersmay include adjusting spark timing to increase combustion stabilityduring the water ingestion (e.g., water release from CAC). For example,the controller may advance spark timing during a tip-in (e.g., pedalposition greater than an upper threshold position) when the waterrelease rate and/or water release amount are greater than theirrespective thresholds. In another example, the controller may retardspark timing if the pedal position is relatively constant, or below athreshold position, when the water release rate and/or water releaseamount are greater than their respective thresholds (e.g., during acondensate purging routine). The amount of spark retard or advance maybe based on the water release rate and/or the water release amount. Inother examples, additional or alternative combustion parameters may beadjusted during the water release conditions.

Alternatively at 303, if the water storage rate is positive, the methodcontinues on to 304 to determine if the water storage rate (e.g.,condensate storage rate or water accumulation rate in the CAC) isgreater than a threshold rate. In one example, the threshold waterstorage rate may be based on a rate at which a threshold amount ofcondensate may accumulate in the CAC. The threshold amount of condensate(or water) may result in engine misfire or unstable combustion if blownout of the CAC at once and ingested by the engine. If the water storagerate is greater than the threshold rate, the method continues on to 306to decrease cooling efficiency of the CAC. Decreasing cooling efficiencyof the CAC may include one or more of closing or reducing an opening ofvehicle grille shutters, turning off or reducing a speed of an enginecooling fan and/or dedicated CAC fan, and/or decreasing coolant pumpspeed of a coolant-cooled CAC coolant pump. Other engine actuatoradjustments may also be made to decrease the cooling efficiency of theCAC, thereby reducing condensate formation. In one example, thecontroller may adjust the above engine actuators (e.g., fan, grilleshutters, etc.) to increase the CAC temperature above a dew pointtemperature. Alternately or additionally, the EGR rate may be reduced toreduce the condensate formation.

After decreasing CAC cooling efficiency, the method continues on to 308to determine if a water storage amount at the CAC is greater than athreshold amount. As discussed above, the water storage amount may be anamount of condensate or water stored (e.g., built-up) within the CAC. Inone example, the threshold water storage amount may be based on anamount of water that may result in engine misfire and/or unstablecombustion if blown out of the CAC and ingested by the engine all atonce. If the water storage amount at the CAC is greater than thethreshold amount, the method continues on to 310 to purge accumulatedcondensate from the CAC. At 310, the controller may activate variouscondensate purging routines to evacuate condensate from the CAC, basedon engine operating conditions. For example, during a tip-in or otherincrease in engine airflow, the controller may limit an increase inengine airflow to controllably release condensate from the CAC and intothe intake manifold of the engine. In another example, the controllermay increase engine airflow, even if there is not an increased torquerequest, to purge condensate from the CAC. In one example, thecontroller may increase engine airflow by downshifting at transmissiongear. In another example, increasing engine airflow may includeincreasing an opening of a throttle to increase mass air flow. In yetanother example, the purge routine may include activating a condensatepump and a method for disposing of the condensate. The method at 310 mayalso include adjusting additional engine actuators such as spark timing,air-fuel ratio, etc. during the various condensate purging routines.Alternatively, if the water storage amount is not greater than thethreshold amount at 308, the method may continue on to 312 to maintainengine airflow at a requested level and maintain engine operatingconditions.

In this way, the controller may adjust engine actuators to reducecondensate formation at the CAC and/or increase combustion stabilityduring water release from the CAC. The controller may base the engineactuator adjustments on water storage and/or water release (e.g., amountof water in the charge air exiting the CAC) parameters. Further, thecontroller may determine the CAC water storage and/or water releaseparameters based on output from an oxygen sensor positioned downstreamfrom the CAC outlet (e.g., at the outlet of the CAC).

In addition to controlling CAC cooling efficiency and/or combustionparameters, output from the outlet CAC oxygen sensor may be used forvarious diagnostics. In one example, the controller may use oxygensensor output to diagnose alternate models and/or estimates of CACefficiency, CAC condensate, and/or CAC dew point. For example, a waterstorage rate (or amount) determined from the outlet CAC oxygen sensorand ambient humidity may be compared to an expected water storage ratedetermined from one of the CAC condensate models. If the two waterstorage rate estimates are not within a threshold of one another, thecontroller may indicate an error in the condensate model. The controllermay then make adjustments to the model to increase the accuracy.

In this way, an engine method comprises adjusting engine actuators basedon water storage at a charge air cooler, the water storage based on anoutput of an oxygen sensor positioned downstream of the charge aircooler and ambient humidity. In one example, the oxygen sensor ispositioned at an outlet of the charge air cooler. Additionally, thewater storage may be one of a water storage rate within the charge aircooler or an amount of water stored within the charge air cooler.

In one example, adjusting engine actuators based on water storageincludes adjusting one or more of vehicle grille shutters, enginecooling fans, or a charge air cooler coolant pump to decrease a coolingefficiency of the charge air cooler in response to the water storagerate increasing above a threshold rate. In another example, adjustingengine actuators based on water storage includes increasing engineairflow to purge condensate from the charge air cooler in response tothe amount of water stored within the charge air cooler increasing abovea threshold amount. In yet another example, adjusting engine actuatorsbased on water storage includes adjusting one or more of spark timing orengine airflow in response to a water concentration at the charge aircooler outlet increasing above ambient humidity, the water concentrationbased on the output of the oxygen sensor.

In some embodiments, the oxygen sensor may be a variable voltage oxygensensor. In this embodiment, a reference voltage of the oxygen sensor maybe modulated between a first voltage and a second voltage, the secondvoltage higher than the first voltage. Water storage may be based on adifference in pumping current of the oxygen sensor between the firstvoltage and the second voltage and wherein the amount of water iffurther based on ambient humidity. In another example, the oxygen sensormay be operated in a base mode. Further, the water storage may be basedon the output of the oxygen sensor only when EGR is not flowing (orbelow a threshold EGR rate).

In one example, ambient humidity is measured with a humidity sensor. Inanother example, ambient humidity is estimated based on one or more ofintake temperature, intake pressure, or a windshield wiper duty cycle.In yet another example, ambient humidity may be determined based onweather data received from one or more of a weather station, remotedevice, or in-vehicle entertainment and communications system of thevehicle.

FIG. 4 shows a graphical example of adjustments to engine operationbased on water storage at the CAC. Specifically, graph 400 shows changesin an output of an oxygen sensor at plot 402, changes in ambienthumidity at plot 404, changes in CAC water storage based on the oxygensensor output at plot 406, changes in CAC water release at plot 410,changes in EGR flow at plot 412, changes in pedal position (PP) at plot414, changes in spark timing at plot 416, changes in a position ofvehicle grille shutters at plot 418, and changes is mass air flow atplot 420. The oxygen sensor may be positioned at an outlet of the CACand referred to herein as the outlet oxygen sensor. Ambient humidity mayeither be measured with a humidity sensor or estimated based on ambientconditions (e.g., temperature and pressure). As discussed above, in someexamples an additional oxygen sensor (different from the outlet oxygensensor) may be positioned in the intake (e.g., intake manifold) forestimating EGR flow. Additionally, if the outlet oxygen sensor is a VVssensor, the outlet oxygen sensor may be modulated between a firstreference voltage, V1, and a second reference voltage, V2. The firstreference voltage may also be referred to as the base reference voltage.The water concentration at the outlet sensor may be based on the changein pumping current when switching between V1 and V2. In alternateembodiments, if the oxygen sensor is not a VVs sensor, the sensor may bemaintained at a base reference voltage and the oxygen concentration atthe CAC outlet may be determined using a dilution method.

Plot 406 shows changes in water storage in the CAC, the water storagebased on the output from the outlet oxygen sensor and ambient humidity.The water storage shown at plot 406 may include an amount of waterstored in the CAC or a rate of water storage in the CAC. Plot 410 showswater release from the CAC. The water release may be a water releaseamount or rate based off the water storage value (and thus based off theoutlet oxygen sensor output and ambient humidity). At plot 406,substantially zero water storage is shown at the zero line 408. Belowthe zero line 408, the water storage value is negative, therebycorresponding to a positive water release value, as shown at plot 410.

Prior to time t1, water storage in the CAC may be less than a thresholdT1 (plot 406) and water release from the CAC may be less than athreshold T2 (plot 410). Additionally, the pedal position may berelatively constant (plot 414) and the grille shutters may be open (plot418). Before time t1, ambient humidity may be increasing. In oneexample, the ambient humidity may be an estimate of the amount of waterin the charge air entering the CAC. Thus, increasing ambient humiditymay indicate an increasing amount of water in the charge air enteringthe CAC. As a result, the CAC water storage level may be increasingbefore time t1 (plot 406). Also before time t1, the EGR rate may bebelow a threshold T3. In one example, the threshold T3 may besubstantially zero such that the EGR is turned off. In another example,the threshold T3 may be a flow rate greater than zero but small enoughthat the EGR flow may not change the outlet oxygen sensor reading.

At time t1, the CAC water storage level increases above the threshold T1(plot 406). In response, the controller may close the grille shutters(plot 418) to reduce condensate formation in the CAC. In alternateexamples, the controller may adjust alternate or additional engineactuators to reduce condensate formation. For example, the controllermay additionally or alternatively turn off an engine cooling fan at timet1.

Between time t1 and time t2 the CAC water storage level may decrease. Attime t2, the CAC water storage may decrease below the threshold T1 andto a value of substantially zero (plot 406). In response, the controllermay re-open the grille shutters (plot 418). In alternate embodiments,the grille shutters may remain open at time t2. Also before time t2,mass air flow begins to increase. In one example, the controller mayincrease mass air flow based on engine operation. In another example,the controller may increase mass air flow to purge the stored condensatefrom the CAC. As the mass air flow increases, the outlet oxygen sensoroutput also increases. This increase in output may indicate an increasein water in the charge air exiting the CAC. At time t2, the CAC waterstorage value becomes negative and CAC water release begins increasingbetween time t2 and time t3 (plot 410). At time t3, the CAC waterrelease increases above threshold T2. In response, the controllerretards spark timing from MBT (plot 416). The controller may retardspark timing rather than advancing spark timing since pedal positionremains relatively constant at time t3. Retarding spark during the waterrelease from the CAC may increase combustion stability as the engineingests the released water (e.g., condensate). At time t4 the waterrelease from the CAC decreases below the threshold T2 (plot 410). Thecontroller then stops retarding spark (plot 416).

As shown in FIGS. 4A-B, an engine method includes adjusting engineactuators based on a water storage rate at a charge air cooler, thewater storage rate based on an output of an oxygen sensor positioned atan outlet of the charge air cooler and ambient humidity. As shown attime t3, in one example, adjusting engine actuators includes adjustingone or more of spark timing or mass air flow in response to the waterstorage rate being negative. Further, adjusting spark timing includesadvancing spark timing when a pedal position is increasing and retardingspark timing when the pedal position is below a threshold position.

In another example, as shown at time t1, adjusting engine actuatorsincludes adjusting one or more of vehicle grilles shutters, enginecooling fans, charge air cooler cooling fans, or a charge air coolercoolant pump to decrease cooling efficiency of the charge air cooler inresponse to the water storage rate increasing above a threshold rate(e.g., threshold T1). The method may further include estimating a waterstorage amount based on the water storage rate. In yet another example,adjusting engine actuators includes increasing engine airflow to purgewater from the charge air cooler in response to the water storage amountincreasing above a threshold amount.

In this way, an output from an oxygen sensor positioned proximate to aCAC outlet may be used to determine water storage at the CAC. In oneexample, an oxygen sensor positioned at the outlet of the CAC may beused, along with ambient humidity, to determine an amount of waterstored within the CAC. A controller may adjust one or more engineactuators in response to water storage at the CAC (e.g., amount of wateror rate of water accumulation in the CAC). For example, the controllermay adjust vehicle grille shutters, engine cooling fan, and/or an enginecoolant pump to reduce CAC cooling efficiency in response to a waterstorage amount or rate above a threshold. In yet another example, thecontroller may adjust engine airflow via adjusting a throttle and/ordownshifting operations to purge condensate from the CAC in response tothe water storage amount increasing above a threshold. In this way, atechnical result of determining water storage at the CAC from an oxygensensor and ambient humidity may be achieved, thereby reducing CACcondensate formation and increasing combustion stability.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory. The specific routinesdescribed herein may represent one or more of any number of processingstrategies such as event-driven, interrupt-driven, multi-tasking,multi-threading, and the like. As such, various actions, operations,and/or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedactions, operations and/or functions may be repeatedly performeddepending on the particular strategy being used. Further, the describedactions, operations and/or functions may graphically represent code tobe programmed into non-transitory memory of the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. An engine method, comprising: using engineactuators to adjust engine operation based on water storage at a chargeair cooler, the water storage determined based on an output of an oxygensensor positioned downstream of the charge air cooler and ambienthumidity.
 2. The method of claim 1, wherein the oxygen sensor ispositioned at an outlet of the charge air cooler.
 3. The method of claim1, wherein the water storage determination is based on the output of theoxygen sensor only when EGR is not flowing.
 4. The method of claim 1,wherein ambient humidity is measured with a humidity sensor.
 5. Themethod of claim 1, wherein ambient humidity is estimated based on one ormore of intake temperature, intake pressure, or a windshield wiper dutycycle.
 6. The method of claim 1, wherein ambient humidity is determinedbased on weather data received from one or more of a weather station,remote device, or in-vehicle entertainment and communications system. 7.The method of claim 1, wherein the oxygen sensor is a variable voltageoxygen sensor and further comprising modulating a reference voltage ofthe oxygen sensor between a first voltage and a second voltage, thesecond voltage higher than the first voltage.
 8. The method of claim 7,wherein water storage determination is based on a difference in pumpingcurrent of the oxygen sensor between the first voltage and the secondvoltage and wherein the water storage determination is further based onambient humidity.
 9. The method of claim 1, wherein the water storage isone of a water storage rate within the charge air cooler or an amount ofwater stored within the charge air cooler.
 10. The method of claim 9,wherein adjusting engine operation based on water storage includesadjusting one or more of vehicle grille shutters, engine cooling fans,or a charge air cooler coolant pump to decrease a cooling efficiency ofthe charge air cooler in response to the water storage rate increasingabove a threshold rate.
 11. The method of claim 9, wherein adjustingengine operation based on water storage includes increasing engineairflow to purge condensate from the charge air cooler in response tothe amount of water stored within the charge air cooler increasing abovea threshold amount.
 12. The method of claim 9, wherein adjusting engineoperation based on water storage includes adjusting one or more of sparktiming or engine airflow in response to a water concentration at anoutlet of the charge air cooler increasing above ambient humidity, thewater concentration based on the output of the oxygen sensor.
 13. Anengine method, comprising: using engine actuators to adjust engineoperation based on a water storage rate at a charge air cooler, thewater storage rate determined based on an output of an oxygen sensorpositioned at an outlet of the charge air cooler and ambient humidity.14. The method of claim 13, wherein adjusting engine operation includesadjusting one or more of vehicle grilles shutters, engine cooling fans,charge air cooler cooling fans, or a charge air cooler coolant pump todecrease cooling efficiency of the charge air cooler in response to thewater storage rate increasing above a threshold rate.
 15. The method ofclaim 13, further comprising estimating a water storage amount based onthe water storage rate and wherein adjusting engine operation includesincreasing engine airflow to purge water from the charge air cooler inresponse to the water storage amount increasing above a thresholdamount.
 16. The method of claim 13, wherein adjusting engine operationincludes adjusting one or more of spark timing or mass air flow inresponse to the water storage rate being negative.
 17. The method ofclaim 16, wherein adjusting spark timing includes advancing spark timingwhen a pedal position is increasing and retarding spark timing when thepedal position is below a threshold position.
 18. An engine system,comprising: an intake manifold; a charge air cooler positioned upstreamof the intake manifold; an oxygen sensor positioned at an outlet of thecharge air cooler; and a controller with computer readable instructionsfor adjusting engine operation responsive to water storage at the chargeair cooler, the water storage determined based on an output of theoxygen sensor and ambient humidity when exhaust gas recirculation is notflowing.
 19. The system of claim 18, wherein adjusting engine operationincludes one or more of adjusting spark timing, mass air flow, vehiclegrille shutters, engine cooling fans, a charge air cooler coolant pump,or downshifting a transmission gear.
 20. The system of claim 18, whereinwater storage includes one or more of a water storage amount in thecharge air cooler or a water storage rate in the charge air cooler.